Biodiesel production via transesterification of canola oil in the presence of NaeK doped CaO derived from calcined eggshell Maryam Khatibi a , Farhad Khorasheh a , Afsanehsadat Larimi b, * a Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran b Department of Chemical and Process Engineering, Niroo Research Institute, Tehran, Iran article info Article history: Received 5 May 2020 Received in revised form 30 September 2020 Accepted 7 October 2020 Available online 14 October 2020 Keywords: Biodiesel NaeK/CaO Transesterification Canola oil Eggshell abstract CaO derived from calcined eggshell was doped with NaeK by wet impregnation method and the effect of different Na/K molar ratios was investigated on biodiesel production from canola oil. The catalysts were characterized by X-ray Powder Diffraction (XRD), BrunauereEmmetteTeller (BET), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Thermogravimetric (TGA) analyses. FAME yields were determined by Gas Chromatography-Mass Spectrometry (GC-MS). The NaeK/CaO catalyst with Na/ K molar ratio of 1 showed the highest FAME yield of 97.6% at optimum reaction conditions. Structural investigation of materials revealed that FAME yield was proportional to the number of basic sites on the surface of catalyst. The optimum reaction conditions were found to be catalyst loading of 3 wt%, methanol to oil molar ratio of 9:1, reaction temperature of 50  C, and reaction time of 3 h. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction About 85% of the world’s energy demand is currently met by conventional fossil fuels whose reserves are constantly decreasing [1]. A major problem with the use of fossil fuels is greenhouse gas (GHG) emission that is responsible for global warming [2]. There have been concerns in the social, political, and commercial contexts about the availability of fossil fuel energy in the quantities needed by industrial societies [3]. According to an estimate, conventional fossil fuel sources will remain the main energy source for at least the next 20e30 years [4]. It is now time to consider other sus- tainable and renewable fuels such as biofuels (bioethanol, bio- diesel, biogas, etc.) that could reduce greenhouse gas emissions and be an appropriate alternative to diesel fuel [5]. Among the various biofuels, biodiesel is one of the best alternative energy sources since it is clean, renewable, biodegradable, non-toxic, environ- mentally friendly, and it can be produced from a variety of renewable sources [6]. It has also been reported that the chemical and physical properties of biodiesel (such as higher lubrication quality and lower sulfur content) are better than conventional diesel produced from fossil fuels [7]. Biodiesel production cost, however, is high. The cost of biofuels is approximately 1e 1.5 times higher than that of fossil fuels with the performance and price of biodiesel strongly dependent on the catalyst choice [8]. Homogeneous and heterogeneous catalysts can both catalyze the reactions for biodiesel production with a similar reaction mechanism. The mechanism of catalytic transesterification reaction is described by the disassociation of catalyst and methanol to release CH₃O (methoxide anion) from the reaction of methanol (CH₃OH) and a hydroxide ion (OH  ). The carbonyl carbon of the triglyceride is attacked by the anion (CH₃O) in three steps to pro- duce a mole of methyl ester along with di-glyceride and/or mono- glyceride in the first and second step. Finally, after the third step, 3 mol of methyl ester and a mole of glycerol are formed [9]. The most common homogeneous alkali catalysts are potassium hy- droxide (KOH), potassium methoxide (KOCH₃), sodium hydroxide (NaOH), sodium methoxide (NaOCH₃), and sodium ethoxide (NaOCH₂CH₃). Sulfuric acid (H₂SO₄), sulfonic acid, hydrochloric acid, organic sulfonic acid, and iron sulfate are the most widely used acids as homogeneous catalyst in transesterification [10]. Compared with heterogeneous catalysts, homogeneous catalysts have higher activity [4] and faster reaction rates with reactions occurring at relatively milder conditions [11]. Homogeneous cata- lysts, however, are more difficult to be separated from the reaction media to be reused [12], produce wastewater during the down- stream processing [13], and require expensive equipment due to * Corresponding author. E-mail addresses: afsaneh.larimi@gmail.com, alarimi@nri.ac.ir (A. Larimi). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene https://doi.org/10.1016/j.renene.2020.10.039 0960-1481/© 2020 Elsevier Ltd. All rights reserved. Renewable Energy 163 (2021) 1626e1636